The present invention relates to a method of laser marking which is used to form on a surface of an article a sharp mark by means of laser beam at high speed.
In forming marks such as a symbol mark, configuration of product and manufacturing data of product, etc., on a surface of an article, it has been usual to use the so-called mask transfer technique by which a plurality of symbols and/or characters are transferred onto such surface simultaneously at high speed or to engrave the surface up to several microns by scanning a laser beam along symbols and/or character to be marked thereon.
Particularly, in the conventional marking method using a laser beam, a portion of the product on which the marking is to be performed by local laser-heating and evaporation of material of the product must be heated to a temperature at which such local evaporation takes place. The temperature depends upon the material of the product and it is about 500.degree. C. when the material is of plastics and about 2000.degree. C. when the material is ceramics.
Therefore, in order to achieve such high temperature of the local portion of the product, an output power of a laser must be large enough. However, when the product is, for example, an electronic component such as a semiconductor device, there is a strong possibility of thermal degradation thereof due to local heating by the laser beam and dust and/or smoke produced during the laser marking may contaminate the electronic component.
Since the marking is performed by the local evaporation and/or burning of the material, the smoothness of the surface of the product may be degraded and the sharpness of the mark formed thereon may become degraded sometimes.